HI Nompancakes, As far as Zyrtec goes, in Canada it is over-the-counter, but is called Reactine. Hope that helps…. No Diamox and flying? My recommendation is a barf bag. ha. Sorry, but we don’t have many options for decreasing our pressure (which is lousy). My son used to faint whenever they changed the cabin pressure. My friend, with hydrocephalus, would vomit and maybe pass out. Yikes. I just didn’t feel well, and couldn’t seem to recover when we landed. That is pretty typical for “us”, I think. On Diamox as needed, it is smooth flying! Yea! I hope you get it in time! 🙂